Tube Production and Assembly Systems: The Impact of Compliance and Variability on Yield

Variation modeling is used in design to predict and diagnose potential quality problems. Most variation modeling assumes the parts are rigidly assembled. However, in some cases, this assumption is invalid. For example, when hydraulic tubes are assembled into aircraft structures, the compliance of the tube facilitates assembly. If the tubes were rigid, they cannot be assembled, i.e., the variations of the tubes and structures are too great. Despite the importance of compliance in assembly, it is typically not explicitly modeled during design. This paper proposes a new method to directly predict the assemblability of any tube design with minimal dependence CAD/FEM modeling and simulation. The model includes a variation model for the tubes and aircraft, compliance model and assembly model. It can be used during design to improve yields

Probing DNA conformational changes with high temporal resolution by Tethered Particle Motion

The Tethered Particle Motion (TPM) technique informs about conformational changes of DNA molecules, e.g. upon looping or interaction with proteins, by tracking the Brownian motion of a particle probe tethered to a surface by a single DNA molecule and detecting changes of its amplitude of movement. We discuss in this context the time resolution of TPM, which strongly depends on the particle-DNA complex relaxation time, i.e. the characteristic time it takes to explore its configuration space by diffusion. By comparing theory, simulations and experiments, we propose a calibration of TPM at the dynamical level: we analyze how the relaxation time grows with both DNA contour length (from 401 to 2080 base pairs) and particle radius (from 20 to 150~nm). Notably we demonstrate that, for a particle of radius 20~nm or less, the hydrodynamic friction induced by the particle and the surface does not significantly slow down the DNA. This enables us to determine the optimal time resolution of TPM in distinct experimental contexts which can be as short as 20~ms.Comment: Improved version, to appear in Physical Biology. 10 pages + 10 pages of supporting materia

JOINING SEQUENCE ANALYSIS AND OPTIMIZATION FOR IMPROVED GEOMETRICAL QUALITY

Disturbances in the manufacturing and assembly processes cause geometrical variation from the ideal geometry. This variation eventually results in functional and aesthetic problems in the final product. Being able to control the disturbances is the desire of the manufacturing industry. \ua0 Joining sequences impact the final geometrical outcome in an assembly considerably. To optimize the sequence for improved geometrical outcome is both experimentally and computationally expensive. In the simulation-based approaches, based on the finite element method, a large number of sequences need to be evaluated.\ua0 In this thesis, the simulation-based joining sequence optimization using non-rigid variation simulation is studied. Initially, the limitation of the applied algorithms in the literature has been addressed. A rule-based optimization approach based on meta-heuristic algorithms and heuristic search methods is introduced to increase the previously applied algorithms\u27 time-efficiency and accuracy. Based on the identified rules and heuristics, a reduced formulation of the sequence optimization is introduced by identifying the critical points for geometrical quality. A subset of the sequence problem is identified and solved in this formulation.\ua0 For real-time optimization of the joining sequence problem, time-efficiency needs to be further enhanced by parallel computations. By identifying the sequence-deformation behavior in the assemblies, black-box surrogate models are introduced, enabling parallel evaluations and accurate approximation of the geometrical quality. Based on this finding, a deterministic stepwise search algorithm for rapid identification of the optimal sequence is introduced.\ua0 Furthermore, a numerical approach to identify the number, location from a set of alternatives, and sequence of the critical joining points for geometrical quality is introduced. Finally, the cause of the various deformations achieved by joining sequences is identified. A time-efficient non-rigid variation simulation approach for evaluating the geometrical quality with respect to the sequences is proposed. \ua0 The results achieved from the studies presented indicate that the simulation-based real-time optimization of the joining sequences is achievable through a parallelized search algorithm and a rapid evaluation of the sequences. The critical joining points for geometrical quality are identified while the sequence is optimized. The results help control the assembly process with respect to the joining operation, improve the geometrical quality, and save significant computational time

Microassembly technology for modular, polymer microfluidic devices

Assembly of modular, polymer microfluidic devices with different functions to obtain more capable instruments may significantly expand the options available for detection and diagnosis of disease through DNA analysis and proteomics. For connecting modular devices, precise, passive alignment structures can be used to prevent infinitesimal motions between the devices and minimize misalignment. The motion and constraint of passive alignment structures were analyzed using screw theory. A combination of three v-groove and hemisphere-tipped post joints constrained all degrees of freedom of the two mating modules without overconstraint. Simulations and experiments were performed to assess the predictability of dimensional and location variations of injection molded components. A center-gated disk with micro scale assembly features was replicated. Simulations using a commercial package (Moldflow) overestimated replication fidelity. Mold surface temperatures and injection speeds significantly affected the experimental replication fidelity. The location of features for better replication, at each mold surface temperature, moved from the edge of the mold cavity to the injection point as the mold surface temperature increased from 100˚C to 150˚C. Prototype modular devices were replicated using double-sided injection molding for the experimental demonstration. Dimensional and location variations of the assembly features and alignment standards were quantified for an assembly tolerance analysis. Monte Carlo methods were applied to the assembly tolerance analysis to simulate propagation and accumulation of variation in the assembly. In simulations, mean mismatches with standard deviations ranged from 115±29 to 118±30 µm and from 17±11 to 19±13 µm along the X- and Y-axes, respectively. Vertical gaps with standard deviations at the X- and Y-axes were 312±37~319±37 µm, compared to the designed value of 287µm. The measured lateral mismatches were 103±7~116±11 µm and 15±9~20±6 µm along the X- and Y-axes, respectively. The vertical gaps ranged from 277±4 µm to 321±7 µm at the X- and Y-axes, respectively. The present study combined an investigation of microassembly technology with a better understanding of the micro injection molding process, to assist in realizing cost-effective mass production of modular, polymer microfluidic devices enabling biochemical analysis

The dimensional variation analysis of complex mechanical systems

Dimensional variation analysis (DVA) is a computer based simulation process used to identify potential assembly process issues due the effects of component part and assembly variation during manufacture. The sponsoring company has over a number of years developed a DVA process to simulate the variation behaviour of a wide range of static mechanical systems. This project considers whether the current DVA process used by the sponsoring company is suitable for the simulation of complex kinematic systems. The project, which consists of three case studies, identifies several issues that became apparent with the current DVA process when applied to three types of complex kinematic systems. The project goes on to develop solutions to the issues raised in the case studies in the form of new or enhanced methods of information acquisition, simulation modelling and the interpretation and presentation of the simulation output Development of these methods has enabled the sponsoring company to expand the range of system types that can be successfully simulated and significantly enhances the information flow between the DVA process and the wider product development process

Dimensional variation analysis of deformable aluminium-intensive vehicle assemblies

The thesis concerns dimensional management and the provision of tools and techniques to assist designers and body engineers in the automotive industry with the tolerance specification and variation analysis of deformable aluminium-intensive vehicle (AIV) assemblies. [Continues.

Validation of a tolerance analysis simulation procedure in assemblies

A simulation of tolerance analysis in assemblies using Sigmund Computer Aided Tolerancing (CAT) software is validated through the example of an automobile locking device. Simulation with CAT, applying criteria on both the statistical distribution and the rivet pin position in the hole used in the example, will allow us to predict the functional dimension tolerances in these assemblies with greater accuracy in the preliminary design phase. These tolerances will subsequently define the manufacturing specifications. The statistical distribution, in the example, that best fits the overall set of tolerances, is the triangular distribution followed by the normal distribution; the position of the rivet pin axis in its hole is off-centre by 53 % with regard to its maximum value

Allocation of geometric tolerances in one-dimensional stackup problems

Many tolerancing problems on mechanical assemblies involve a functional requirement depending on a chain of parallel dimensions on individual parts. In these one-dimensional cases, simple methods are available for the analysis and the allocation of dimensional tolerances. However, they are difficult to extend to geometric tolerances, which must be translated into equivalent dimensional tolerances; this allows the analysis but makes the allocation generally impossible without Monte Carlo simulation and complex search strategies. To overcome this difficulty, the paper proposes a way of dealing directly with geometric tolerances in the allocation problem. This consists in expressing the functional requirement as a linear model of geometric tolerances rather than equivalent dimensional tolerances; the coefficients of the model (sensitivities) are calculated considering both the dimension chain and the standard definition of the geometric tolerances. The approach can be combined with any constrained optimization method based on sensitivities. The optimal scaling method, previously proposed for dimensional tolerances, is extended to geometric tolerances and used in two examples to demonstrate the simplicity of the overall workflow and the quality of the optimal solution